The wax crystals that precipitate from diesel fuels in cold weather have always created problems for drivers and distributors. Left untreated, they form relatively large flat plates which rapidly gel the fuel and block lines. Treated with conventional additives, they flow freely and form wax cakes, often permeable, on diesel vehicle main filters and thus a delicate balance exists between running freely and blocking the filters. Chemical and engineering research has lead to the creation of an additive system which modifies the sizes and shapes of these wax crystals down to micron sizes and enables them to pass through such filters. This creates an opportunity for trouble free operation at very low temperatures in fuels which it was previously impossible. Passage of the wax crystals through the filters can provide a vehicle operability level of up to 30°C below the initial crystallisation temperature.